PLATE 2 



EXPLANATION OF FIGURES 



14 Section through the forebrain of a head-meroplast showing aniagen of 

 the ventral aorta. The longitudinal incision on the right was relatively close 

 to the neural fold. The cut edges of the pharyngeal entoderm have pulled apart 

 the ventral tissues having swung to the left. Experiment, Type I, no. 31 (X 240). 

 b, ventral aorta; c, coelom; d, pharynx; e, forebrain. 



15 Section through the forebrain of a head-meroplast showing a well-defined 

 ventral aorta. The right longitudinal incision was close to the neural fold. 

 None of the excised head has regenerated; the mesenchjane is very compact 

 near the cut surface the cells of which are somewhat epithelial. Total incuba- 

 tion thirty-three hours. Operation at the time of the first intersomitic groove 

 (X 175). Type 1, no. 17; b, ventral aorta; c, coelom; d, pharynx; e, forebrain. 



16 Section through the forebrain of a head-meroplast showing a proamniotic 

 sac containing a pouch of coelomic mesothelium. On the ventral side of the 

 sac is a peculiar proliferation of entodermal cells very constantly appearing in 

 experiments of this type, generally more s^nrnmetrically situated. Total incu- 

 bation, forty-eight hours. Operation at the time of the second intersomitic 

 groove (X 55). Experiment, Type II, no. 3; c, coelom; e. forebrain;/, ectoderm; 

 g, entoderm; J, extra-embryonic vessels. 



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